This invention relates to the art of compression tools for joining pipes and couplings and, more particularly, to improvements by which a failure of one or both pivotal jawarm members of a compression jawset is indicated to a user thereof.
A compression tool of the character to which the present invention relates is shown in U.S. Pat. No. 6,434,998 to Amherd. Such tools include a compression jawset removably mounted on a drive mechanism by which the jawarms of the set are displaced into compression about a pipe and coupling to join the latter. The jawset is comprised of a pair of jawarm members pivotally mounted between a pair of side plates and having laterally inwardly open opposed jaw recesses at one end and laterally inwardly facing cam surfaces at the opposite ends. The jawarms are pivotal about pins located in openings through the jawarms between the opposite ends thereof, and the jawarm members have laterally inner and outer edges between the opposite ends thereof. The inner edges of the jawarms have inwardly open opposed spring pin and spring recesses which accommodate a spring pin and a spring extending across the forward end of the pin and having legs extending rearwardly along the inner surface of the corresponding jawarm, whereby the jawarms are biased toward the closing direction relative to workpieces to be joined together. The jawset is mountable on the drive mechanism by means of the side plates and at a location relative to the jawset which is laterally between the pivot pins and cam surfaces of the jawarms. The drive mechanism includes cam rollers which are displaceable axially forwardly and rearwardly along the cam surfaces of the jawarms, and when displaced forwardly of the cam surfaces, the cams engage the latter and displace the opposed jaw recesses toward one another and constrictably about a pipe and coupling interposed therebetween. During operation of the jawset to compressibly join a pipe and coupling, the area of each of the jawarm members between the pivot pin opening and inner edge thereof and along the inner edge between the jaw recess and cam surface thereof is under tension, and the area of the jaw arm laterally outwardly of the pivot pin opening is under compression. The side plates are also stressed during operation of the jawset in that pivotal displacement of the jawarm members about the pivot pins to produce compressive engagement between the jaw recesses imposes laterally outwardly directed forces through the pivot pins to the side plates.
At some point during the life of the jawset, failure will occur. Such failure may be in a side plate of the jawset or in a jawarm member. With respect to failure in a jawarm member, the latter is initiated by a fatigue crack at a location along the inner edge thereof and fracture of the jawarm from the fatigue crack toward the outer edge thereof. In the absence of intentionally designed structures for controlling the location of the fatigue crack and the direction of the fracture therefrom, as shown for example in co-pending patent application Ser. No. 10/364,008 filed Feb. 12, 2003 and assigned to the same assignee as the present application, the disclosure of which is incorporated herein for background information, the location of the fatigue crack and direction of the fracture is unpredictable. In testing 38 jawarm members of different sizes and of the structure shown in the patent to Amherd, it was noted that a majority of the jawarms of each size either failed from the spring pin recess to the pivot pin opening through the jawarm or from the spring pin recess across the jawarm towards the outer edge thereof. Moreover, such failures outwardly of the spring pin opening are not visible to a user of the compression tool in that the spring pin and pin recesses and areas of the jaw arm outwardly thereof are covered by the side plates of the jawset. Accordingly, by the time a user of the compression tool becomes aware of such failure, a number of unacceptable, oversized crimps can be made, and the replacement thereof is unnecessarily time-consuming and expensive. The pin spring biases the pin rearwardly of the pin opening defined by the opposed pin recesses, and deformation of the jawarm following a fracture will be such that the recesses will spread apart sufficiently for the spring to eject the pin from the pin opening. While this visually indicates a failure to the user of the compression tool, such deformation to the extent necessary for ejection of the pin is preceded by the making of a number of unacceptable, oversized crimps.